Things have been going great with the Firebird I installed my 79 Trans am posi axle and put 3.73 gears in at the same time test drive went great no noises from the new axle and she lights up both rear wheels now!

I ordered a speedo drive for a TH350 off ebay and it arrived yesterday so I tried to fit it but it's too small the one thats in there has a longer shaft about 1/2" where the speedo cable goes in and the gear is much larger.

I ordered a 24 tooth for my 3.73 gears for a TH350 which is what I'm running and it there see pic. My speedo is wayout it reads 50mph when I'm doing about 30! Anyone have any ideas

Here is the speedo gear I ordered
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=260022106240&viewitem=&sspagename=STRK%3AMEWNX%3AIT

Check out the B&M and/or TCI websights. They have the info you need.

Probably need the other sleeve.

See the charts on this page: http://chevelleengineer.home.comcast.net/~chevelleengineer/speedo.htm

Thanks for the replies Guys I have found from the the Chevelle web site that I have a BOP TH350 with a large speedo housing that expains why the gear I ordered was too small.

I have a white gear in there and all I need to do now is take it out again and measure it more accurately and count how many teeth I have. Then I need to work out my speedo error and esatblish how many teeth I need.

I took the gear out again yesterday and photographed it with my mobile phone and measured it. It's was orange not white as I said before and it has 35 teeth.

I have contacted the guy I bought my speedo gear from Ebay and he says I have the large housing and orange gear goes from 34 to 39 teeth. He says that one tooth larger corects for about 3.5 mph. I am about 20 mph out at 40 mph as my speedo is reading about 60 mph when I matched my speed with other cars in a 40 mph speed limit so this is only a rough estimate of how far out the speedo is.

When I was in a 70mph limit I matched my speed with other cars and my speedo was reading 100mph and when I went about 80mph it was 120mph. So If I go drag racing I am going to be doing about 95 to 100mph across the line so my speedo will be off the scale! Does it just keep going round or will it break.

He also says that If you I go to a 40 thru 45 you must change the housing too. I also may have to change the drive gear.

I was going to see if I can get a 39 tooth gear as that would correct 17.5mph and that may be close enough.

One thing about these speedos, is the faster you go, the more inaccurate they are. I used an adapter as I had a similar issue with the housings. It got me right on till about 25-30 mph, and it runs about 5 mph slow at about 70...all checked with GPS tracking. I was happy, probably wasn't much more accurate from the factory.

Here is the site I got the adapter from.

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

You just need to find out the percentage you are out and then select from the drop down the closest match. It's the GM / Dodge / Ford Ratio Adapter. This way you avoid taking the trans apart to change the drive gear.